Check engine light came on and my car would not accelerate

My car started first having some issues five days ago. The first sign of trouble was a rattling noise coming from the engine. It sounded like an old diesel engine. The frequency of the rattle would increase as the car accelerates. However,
there was no performance loss and the check engine light did not come on.

The next day, early in the morning, the car started normally (the rattle still present). It drove normally for about five minutes. Then I had to drive up an incline and the car stopped accelerating. It would not drive past three or five mph even on pressing the gas pedal. I immediately stopped the car and while I was trying to figure out what happened, it started driving again normally. But I immediately took it to the nearest auto shop. The following was the diagnosis given by the auto shop:

1. Codes

P0320 - Ignition/distributor engine speed circuit fault.
P1191 - Limp home valve system fault.
P1193 - Limp home valve on low rpm.

However, I had these codes for almost a year now and the car ran without any problem. So, I am not sure if these have got to do with the current issue.

2. Vehicle needs:

a.) Timing belt service.
b.) Tune up (ignition wires frayed by rodents).
c.) Camshaft and crank sensor.

All these are just guesstimates and they told me that in their opinion, it is not worth repairing the car as it is going to cost a lot of money. It seems, even to correctly diagnose the issue, it is going to be expensive. So, they told me to just keep on driving till it dies. They said that apart from the rattling noise, which is still present, the car is drive-able. I have to mention here that I am a full-time student and I cannot afford expensive repairs.

I drove the car without any issues for the three days. The rattling noise was present but there was not any issue with the performance. But today, early in the morning, the car again would not accelerate after running normally for the first three minutes. This time, the check engine light came on and the car would not accelerate beyond three or five mph.

Just two months ago, I got four new tires, replaced the brakes and got a new battery. So, I am sad that all that will go waste if I get rid of my car now.

My question is, looking at my symptoms, is there anyway to guess what might be the issue with my car? If I at least know how much is it going to fix it, I can take a decision to whether fix it or not.

Thank you.